1. Field
The present invention relates generally to medical treatment using focused radiation, and more particularly to planning and/or verification systems used in conjunction with such treatment.
2. Description
Conventional radiation treatment typically involves directing a radiation beam at a tumor located within a patient. The radiation beam is intended to deliver a predetermined dose of treatment radiation to the tumor according to an established treatment plan. The goal of such treatment is to kill tumor cells through ionizations caused by the radiation.
Healthy tissue and organs are often in the treatment path of the radiation beam during radiation treatment. The healthy tissue and organs must be taken into account when delivering a dose of radiation to the tumor, thereby complicating determination of the treatment plan. Specifically, the plan must strike a balance between the need to minimize damage to healthy tissue and organs and the need to ensure that the tumor receives an adequately high dose of radiation. In this regard, cure rates for many tumors are a sensitive function of the radiation dose they receive.
It is therefore necessary to design treatment plans to maximize radiation delivered to a target while minimizing radiation delivered to healthy tissue. Even if such a plan is designed, the goals of maximizing target radiation and minimizing healthy tissue radiation may not be achieved if the radiation is not delivered exactly as required by the treatment plan. More specifically, poor treatment planning and errors in radiation delivery can each result in low irradiation of tumors and high irradiation of sensitive healthy tissue.
In conventional radiation treatment systems, a linear accelerator generates a divergent beam of photons having energies in excess of 1 MeV and the beam is directed toward a treatment area of a patient. The beam may be shaped by beam shaping devices before reaching the treatment area in an attempt to ensure that beam shape closely matches the shape of the treatment area and does not harm healthy tissue. Accordingly, conventional megavoltage treatment is planned by considering the divergence of the beam, the distance over which the beam travels to the treatment area, and known data representing organs and other structures internal to the patient.
A kilovoltage radiation treatment system such as those described in U.S. Pat. No. 6,366,801 to Cash et al produces a divergent beam of traditional medical x-rays having energies in the 50 to 150 keV range and focuses the beam on a target using a lens designed for this purpose. Since the beam follows a path that is quite different from the path followed by megavoltage treatment beams, the above-described conventional systems are not suitable for planning and verification of kilovoltage radiation treatment. It would therefore be beneficial to provide a system for planning and verification of radiation treatment that efficiently accounts for the path of a focused treatment beam.